feat: subscriptions & related changes

[plun1331]

Summary

https://discord.com/developers/docs/change-log#premium-apps-entitlement-migration-and-new-subscription-api

Information

• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed).
• This PR is not a code change (e.g. documentation, README, typehinting,
  examples, ...).

Checklist

• I have searched the open pull requests for duplicates.
• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
• If type: ignore comments were used, a comment is also left explaining why.
• I have updated the changelog to include these changes.

[plun1331]

Untested (because i can't)

[Lulalaby]

@plun1331 if u want to test it lmk, i have a few apps with monitization ready u could use
tho these changes are being made in future, not sure if we should test it rn

[plun1331]

tested

[plun1331]

@Lulalaby review when available please :3

[Lulalaby]

i'm still down with illness

[DA-344]

This now requires the new changes from discord/discord-api-docs#7304 , just a new field.

[Lulalaby]

If you mean the country field, as noted by discord, it's only available through a private oauth scope. So I'm not sure if it's needed 😅

[DA-344]

I meant the renewal_sku_ids field 😅

[Lulalaby]

Oop. Missed that. I only proof-readed the discord pr 😅